If Gundam Seed is recent enough, then definitely that. Many interesting characters, and a rivaly that doesn't suck. A lot of people hate the 2nd part, "Destiny", since it focuses on a weak character and not necessarily even a protagonist but I think it contrasts perfectly with Kira's experience in the first series and the reason he later disappears. Mech design is top notch as well.

Gundam 00 was the last really good one I've seen. I really need a mecha fix.

Yeah no kidding.

Recently I've watched Viper's Creed which is OK. The mech portion of it is kind of minor though.

Then there is Infinite Stratos, but that's also a harem anime, so you've got to deal with that, and the fact that it is only 12 episodes and with ongoing disputes with its author there isn't going to be any resolution anytime soon.

I've been meaning to check out Broken Blade. It starting airing in winter, and then there's a few interesting mecha anime coming out this spring as well.

Check out Gargantia, which has just started airing. It was an amazing first episode even for the non-sci fi/mecha fans. But I'm a sci-fi/mecha fan. so I realllyy enjoyed it, had me at the edge of my seat the entire time.